Here are three dex based assassin builds that I came up with. The first one is human and seems to be the most optimal way to build a human as they are somewhat limited in what is worth spending AP on. It has an emphasis on burst/situational dps with past life sneak of shadows, human damage boost, and no mercy. The other two are halfling, which has more flexibility in what it emphasizes due to having a useful racial tree and having to decide how to distribute AP among acrobat, harper, and halfling. The first halfling version has a strong emphasis on sustained, non-situational offense, while the second emphasizes defense. All three of them are not that far apart in either offense or defense, but each does tend to have a different focus. They each use the same gear setup and have the same destiny and twists. I'm also including in this post the gear set I used as int based, which is just as viable as the one listed in the builds below. I'm still undecided about which build I like best and will be TRing into. Any and all feedback is appreciated. Thanks in advance.
Human with a burst/situational dps focus
Halfling with a sustained dps focus
Halfling with a defensive focus
Here is an alternate gear set which essentially uses the same one I had as int based and simply slots 2 dex in the Mysterious Cloak. I would include the Mysterious Cloak in either setup because, as dex based, I lose heal amp from both harper and human. This is a way to maintain the same heal amp and only lose 5 exceptional seeker. The Mysterious Cloak also gains protection 8, for whatever that's worth. Here is how the dex based gear set listed in the builds compares to the int set listed below:
Gain: con2, dex2, UMD5, vitality20
Lose: proof against poison10, proof against disease10, protection8, underwater action, true seeing, int4, bluff5, PRR6, MRR6
So it's a net gain of 48 hp and 1 DC for a loss of 5 bluff and 6 PRR. All the other stuff is largely irrelevant. The extra 6 PRR from the second setup gives me an additional 2% damage reduction, so I opted for the extra hp from the first setup to make up for the loss of toughness/epic toughness. Some may prefer to use this gear setup and I think they are close enough that neither one has any significant advantages over the other. So I'll include it here for reference for those interested.
Gear Set:
Weapons:
mainhand: Thunder-Forged Dagger (1st degree burns/dragon's edge/mortal fear/orange slotted deconstructor/colorless slotted heal15)
offhand: Assassin's Kiss (greater incorporeal bane/improved deception/greater dispelling/assassination6/purple slotted positive spell power138/mythic weapon boost2)
ranged: Thunder-Forged Throwing Dagger (touch of flames/dragon's edge/mortal fear/orange slotted ruby of endless night/colorless slotted)
Armor: Shadowscale light armor (shadow phase x3/deathblock/ghostly/fort130/2d6 sneak attack/profane reflex1/blue slotted max dex2/green slotted golem's heart)
Goggles: EH Intricate Field Optics with resistance ritual (int3/spot20/TS/green slotted HP40/colorless slotted vitality/alchemical saves1)
Helm: Epic Muffled Veneer (assassinate DC2/hide20/move silently20/spot20/insight reflex2/blue OR yellow slotted Globe of True Imperial Blood/green slotted con2)
Neck: Shroud of Ardent (AC8/sheltering30/blurry/fear immunity/heal amp60/blue OR yellow slotted str6/green slotted good luck2)
Trinket: Epic Litany of the Dead (turn the page/profane abilities2/attack4/damage4/light of dawn/yellow slotted underwater action/green slotted proof against poison10)
Cloak: Mysterious Cloak (heal amp45/MRR25/green slotted protection8/colorless slotted dex2)
Belt: Epic Belt of Thoughtful Remembrance (deathblock7/con11/concentration20/resistance11/dodge11/greater regen/blue slotted natural armor8/green slotted proof against disease10)
Ring swap: Consuming Darkness (seeker12/combat expertise5/green slotted sonic resistance40)
Gloves: EE Backstabber's Gloves (bluff20/sneak attack5/exc sneak3/improved deception/yellow slotted draconic soul gem)
Boots: GS HP Smoke2 boots (45HP/dex skills6/blur/displacement clicky x2)
Ring: Epic Eye of the Beholder (int11/wizardry10/deathblock7/absorb doomsphere spells8/blue OR yellow slotted wis8/green slotted wis2)
Bracers: Epic Ethereal Bracers (dex11/ghostly/riposte9/insight AC5/insight saves4/deadly10/speed14/feather falling/blue OR yellow slotted blindness immunity/green slotted cha2)
Quiver: Epic Quiver of Alacrity (concentration -50/ranged speed15/ranged and spell threat -15/insightful sneak4/doublestrike8)